For the purposes of this application the terminology Voice over Internet Protocol (VoIP) or telephony are not limited to voice but could be any media, including for example voice, video, instant messaging, combinations of voice and video etc.
For the purposes of this application, the terminology of Public and Private Network are intended to encompass not only truly public or private networks, but may also include enterprise or any network where the IP address space are either private or not. However, the distinction between Public and Private is obviously relative and Private networks are generally more private than Public networks.
Utilising traditional circuit switch technology, telephony VPNs have been available for a considerable time. However, the underlying technology of such telephony VPNs is based on circuit switched, i.e. time division multiplex (TDM) class 4 and class 5, switches and this technology is not conducive to the deployment of carrier hosted telephony VPN service to multi-site enterprises. Today, enterprises demand telephony VPN services from carriers, these services including private dial plans, and VoIP calls, etc between enterprise sites. However, where the enterprise sites are located beyond a serving area of a carrier hosted circuit switch, the carrier (service provider) is forced to implement these telephony VPN services between different TDM switches. As a result, a multi site enterprise solution results in a complicated per user dial plan configuration between geographically diverse circuit switches and requires the “cloning” of per enterprise configuration data on each enterprise switch. This dramatically increases the operating expenses for each enterprise receiving a telephony VPN service from the service provider (SP).
In addition to geographical (distance) limitations, political limitations have also played a role in adding to the complexity of multi-site enterprise telephony VPN solutions. Enterprises having sites located in more than one country present greater technical challenges to circuit switched technologies in providing said enterprise with a telephony VPN solution. Carrier hosted telephony VPN solutions require either a single operator with circuit switches in each country where the enterprise has a site, with the switches being located close to said sites, or collaboration between multiple service providers to configure the enterprise telephony VPN between the networks of all the service providers in involved. Even if this arrangement could be achieved thus overcoming the geographical limitations of circuit switched technology, it is not possible for a traditional TDM circuit switch to provide telephony VPN service in more than one country simultaneously.
IP telephony technology provides a separation of media path control from call processing logic. As a result, the devices that send and receive media (referred to generically as media endpoints) can be placed geographically distant from the network intelligence call processing logic (referred to generically as a call agent (these are also sometimes referred to as MGC, Softswitch, SIP Proxy etc.)). As a result of this removal of the geographical limitations encountered with TDM circuit switched technology, in an IP network a single call agent can provide call processing logic services to media endpoints located at large geographical distances from the call agent. So, for example, an enterprise that may have been previously serviced by multiple circuit switches for geographical reasons, can now be populated with suitable media endpoints (either in the enterprise network or in the service provider network) in order to provide telephony media capability at each enterprise site, and by a single call agent located anywhere in the service provider network. Such an arrangement allows a service provider, when deploying carrier hosted services to enterprises, to consider whether or not a single enterprise should be serviced by a single call agent and, if so, which one of the call agents of the service provider network should be utilised, or if a single enterprise should be serviced by multiple call agents and, if so, which ones. With TDM circuit switch technology, such choices are typically not possible. Consequently, the number of call agents employed in a service provider network to service a single enterprise telephony VPN can be reduced to a small number and possibly only one with a consequent reduction in the operating expenses for such enterprise.
Although IP telephony technology has eliminated the above mentioned geographical limitations, political (country) boundaries remain a problem. In order to place a call agent in a single country but providing service to media endpoints in multiple other countries, a number of technical problems need to be addressed. These problems include the need for the call agent to separately apply as appropriate the dial plans of the various enterprises receiving telephony VPN services from the service provider through said call agent and similarly to separately apply the different dial plans of the public service telephone networks (PSTNs) of the various countries in which the various enterprises being serviced have sites. As such, the call agent must be able to interwork the dialing plans of multiple countries when telephony calls over an enterprise telephony VPN traverses multiple countries. Further, the call agent must have the ability to identify a particular country associated with a particular site of an enterprise where such enterprise has sites in various countries. Also, the Call Agent must be able to simultaneously interwork to the PSTN signalling systems in each country, as well as to each country's regulatory service requirements.